The assessment of perceptual capacities generally requires measurement of the subject's ability to integrate information from more than one stimulus dimension. Judgments of this kind are susceptible to various biases arising from cognitive, motivational, and other context effects, often invalidating the measurement. A general methodology, known as functional measurement theory, is being developed to deal with this problem in behavioral information processing. A study is under way to evaluate the usefulness of the functional measurement approach in assessing perceptual constancy judgments. These judgments involve the integration of size and distance information and are known to be affected by attitudinal biases. The question to be answered is whether the functional measurement procedure will result in reliable and valid estimates of perceptual ability, particularly for individual subjects. The data are currently being collected. BIBLIOGRAPHIC REFERENCES: Carlson, V.R.: How Are You Coming Through? In Ferry, T.S. and Weaver, D.A. (Eds.): Directions in Safety. Springfield, Ill., Charles C. Thomas, 1976, pp. 437-446. Carlson, V.R.: Instructions and Perceptual Constancy Judgments. In Epstein, W. (Ed.): Stability and Constancy in Visual Perception. New York, John Wiley & Sons, 1977, pp. 217-254.